Brief Summary

Adelges cooleyi, the Cooley spruce gall adelgid, is a species of aphid-like insects in the order Homoptera, native to forests in the rocky and cascade mountain ranges of the west coast of North America. These insects have a complex life cycle that takes two years and six generations to complete, and involves two host plants. In the fall, nymphs settle to overwinter on their primary host, Picea (spruce trees). They attack Cooley spruce, and also blue spruce to a lesser degree. They lay eggs in the spring, which hatch into nymphs, which, as they start eating at the base of the needles, inject saliva that induces the spruce to form a pinkish colored pineapple-shaped gall. This gall houses them until they emerge as winged (in the case of the females) adults. These then migrate to the adalgid’s secondary host species, Douglas fir (Pseudotsuga), where they eat the needles but do not form a gall structure. The damage done to spruce is mostly aesthetic; it causes branches to misform and causes necrosis where the galls form. Large infestations on Douglas fir can cause foliage discoloration and loss of needles, which is damaging in Christmas tree plantations as well as nursery stock.